The Pentagon is threatening legal action against a former US navy Seal who has written a firsthand account of the raid that killed Osama bin Laden. In a letter addressed to Mark Owen, the writer's pseudonym, lawyers from the US defence headquarters say the book he is about to release violates agreements not to divulge classified information.

The Pentagon's top attorney also warns it is considering legal options against anyone "acting in concert" with the author to publish the book.

No Easy Day cover. Photograph: AP/Dutton

The letter identifies two separate non-disclosure agreements the Seal signed with the navy that legally committed him to never divulge official secrets. "You are in material breach and violation of the non-disclosure agreements you signed," said the letter by Jeh Johnson, the Pentagon's general counsel.

"The department of defence is considering pursuing against you, and all those acting in concert with you, all remedies legally available to us in light of this situation."

US officials had earlier said they were surprised by the book and that it had not been vetted by government agencies to ensure no secrets were revealed. The book has received widespread media coverage and the Pentagon letter notes that some copies have already been released, even ahead of the book's formal release next week.

"Further public dissemination of your book will aggravate your breach and violation of your agreements," the letter warns.

This week the author said in a statement via his publisher that the book was written "with respect for my fellow service members while adhering to my strict desire not to disclose confidential or sensitive information that would compromise national security in any way".

The Pentagon did not release copies of the nondisclosure agreements that it said the author had signed in 2007. A spokesman, Colonel Steve Warren, said they were being withheld because they included the author's real name and his signature.

Other special forces figures have privately expressed disappointment in recent days over the book and the publicity it has received.

An official al-Qaida website has posted a photograph and the real name of the former navy commando, calling him "the dog who murdered the martyr Sheikh Osama bin Laden".